: We have proposed that the primate auditory cortex is organized into three major regions: a core region of three primary-like areas, a belt region containing seven or eight areas bordering the core laterally and medially, and a parabelt region that has at least two subdivisions. Each region represents a successive level of processing, and subdivisions within each region are activated by parallel inputs. The first specific aim is directed at one of the most tentative aspects of this model, which suggests that the medial and lateral portions of the belt region are functionally-distinct. Patterns of cortical and subcortical connections differ between these two regions, and there is compelling electrophysiological evidence of auditory and somatosensory convergence in at least part of the medial belt. We will test the hypothesis that the medial and lateral belt regions mediate different aspects of auditory processing in experiments designed to determine the functional organization of individual fields. Multiunit recordings will be used to identify receptive field properties of neuronal clusters, topographic patterns, and boundaries between subdivisions. These data will guide the placement of neuronal tracers within individual fields to reveal cortical and subcortical connections. The anatomical and physiological data will be combined into functional profiles of each area to evaluate their contributions to auditory cortical processing, in general, and signficance with respect to the general hypothesis. A related issue concerns the extent to which the basic principles of auditory cortical organization in monkeys can be generalized to humans. As a second aim, we will compare architectonic features of auditory cortex in nonhuman primates and humans. Analyses of cytoarchitecture, myeloarchitecture, and the distribution of acetyicholinesterase, cytochrome oxidase, parvalbumin, calbindin, SMI-32, and CAT-301 will be combined to characterize and compare the architecture of core, belt, and parabelt fields in the auditory cortex of monkeys, apes, and humans. As suggested by functional studies in humans and nonhuman primates, we expect to find similarities across species, but important differences may exist that relate to functional specializations. Advancing our understanding of basic auditory cortical organization and processing is essential for continued efforts to evaluate the effects of pathology on auditory function, the capacity for recovery after injury, and the effeSECONDARY